Will Amazon sell Mobipocket books?
Do they already sell it? I haven't seen any.
If they never will, will there be a way to convert their Kindle books to mobipocket?

Well, since Amazon owns Mobipocket and Mobipocket sells books, then idirectly Amazon does sell Mobipocket books. However, you won't find them in the Amazon store. Also, you are better off at Fictionwise or BooksOnBoard since they discount the mobipocket books while Mobipocket doesnt.

For Mobipocket ebooks with DRM there's some method to calulate the Kindle's Mobipocket PID, and registering that with your eBook store will let you download ebooks that will work on your Kindle.

Note that this now only works with "Overdrive" MOBIs from Books on Board and on library ebooks (FictionWise MOBIs probably no longer work), see A Beginner's Guide to Kindle Content. In the Guide, Nate recommends buying LIT and converting to MOBI but, as pdurrant says, mobidedrm works just as well on DRM-laden MOBI ebooks as on AZW ebooks and the resulting DRM-free MOBIs are readable "as is" on a Kindle.

Note that this now only works with "Overdrive" MOBIs from Books on Board and on library ebooks (FictionWise MOBIs probably no longer work), see A Beginner's Guide to Kindle Content. In the Guide, Nate recommends buying LIT and converting to MOBI but, as pdurrant says, mobidedrm works just as well on DRM-laden MOBI ebooks as on AZW ebooks and the resulting DRM-free MOBIs are readable "as is" on a Kindle.

If the book in question has graphics (other then the cover and publisher logo) and there is a LIT edition, there's a chance the graphics in the LIT edition will be larger. So go for the lIT in those cases. Otherwise, the PRC is fine with the DRM stripped.